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Orbital lymphoma

Primary lymphoma of the orbit one of commonest tumours of the orbit and accounts for as much as half of all orbital malignancies.

Epidemiology

Orbital lymphomas account for only 2% of all lymphomas, but constitute 5-15% of all extranodal lymphomas and approximately 50% of all primary orbital malignancies in adults 1,6.

Recently an association between Chlamydia psittaci infection and orbital adnexal MALT lymphoma has been described (MALT-lymphomas account for the majority of orbital lymphomas - see below) 1-2. Infection by Chlamydia psittaci is usually the result of exposure to infected birds and household pets. Patients may go on to develop psittacosis, usually with respiratory tract manifestations 3.

This possible infective aetiology may explain the probably increase in incidence of orbital lymphomas 3.

Typically patients are between 50 and 70 years of age, and no gender predilection is recognised 6.

Clinical presentation

Clinical presentation is variable as any part of the orbit can be involved. In 25% of patients the conjunctiva is involved in which case patients demonstrate a 'salmon red patch' of swollen conjunctiva 1.

The majority of patients who do not have conjunctival involvement (75% of cases) presentation is due to an orbital mass, usually in the superior lateral quadrant, in proximity to the lacrimal gland 1,6:

palpable mass

exophthalmos

ptosis

diplopia and abnormal ocular movement

Generally the mass is painless, however a subset of patients demonstrate inflammatory-like changes with pain, erythaema and swelling 1.

Direct infiltration of the globe and/or optic nerve is rare, and vision is usually preserved 1.

Pathology

Orbital lymphoma is a B-cell non-Hodgkin lymphoma, and in most cases arises from mucosa-associated lymphoid tissue (i.e. orbital adnexal MALT lymphoma (OAML) ): 50-78% of cases in Western nations, and up to 90% of cases from Japan and Korea 1. It is unclear however if MALT exists normally in the conjunctiva of the eye, or whether it represents the sequelae of inflammation (thus the potential link to chlamydial infection). The orbit is otherwise believed to be bereft of lymphatic tissue or lymphatic drainage 1.

Non OAML tumours are of a variety of histologies, with diffuse large B-cell lymphoma being relatively common 4.

Radiographic features

Orbital lymphoma usually appears as a soft tissue mass, either involving the conjunctiva (especially in the case of orbital adnexal MALT lymphoma (OAML) ) or elsewhere in the orbit, frequently in the upper outer quadrant, closely associated with the lacrimal gland.

Although the extraocular muscles may be surrounded or displaced by the mass, they can usually be identified as not being the origin of the tumour, helpful in distinguishing lymphomas from other orbital masses.

Invasion of the globe or optic nerve is rare.

Ultrasound

Content required.

CT

On non-contrast CT, the mass is usually homogeneous in density, either isodense or slightly hyperdense when compared to the extraocular muscles 1. Following administration of contrast, only mild to moderate enhancement is seen, similar again to the extraocular muscles and lacrimal gland.

MRI

Similar to intracranial lymphoma, the densely cellular nature of these tumours with high nucleus-to-cytoplasm ratio results in relatively specific appearances 1,5:

Signal characteristics include:

T1: iso to hypointense to muscle

T2: iso to hyperintense to muscle

T1 C+ (Gd): homogeneous enhancement

DWI: increased signal intensity-restricted diffusion

ADC: reduced values-restricted diffusion

Treatment and prognosis

Orbital adnexal MALT lymphoma (OAML) have a better prognosis than other types of orbital lymphomas, and are not surprisingly more often conjunctival. The recent identification of Chlamydia psittaci as a likely important causative factor in the increasing incidence of orbital lymphomas, has lead to antibiotic therapy being used to not only reduce the size of the tumour, but in some cases result in remission 1-3.

Surgical biopsy/resection, radiotherapy and chemotherapy have all been used and currently no OAML treatment guidelines exist 1. Overall a 65% 5-year relapse-free rate is reported, with less than 5% of patients with OAML eventually dying from the disease 1. Systemic dissemination is only seen in 5-10% of cases 1.

In cases of non-MALT-lymphoma, then similarly a combination of two or more of surgical biopsy/resection, radiotherapy and chemotherapy are usually employed. Prognosis is less favourable.